Merge branch 'zh/ref-filter-atom-type'

The code to handle the "--format" option in "for-each-ref" and friends made too many string comparisons on %(atom)s used in the format string, which has been corrected by converting them into enum when the format string is parsed. * zh/ref-filter-atom-type: ref-filter: introduce enum atom_type ref-filter: add objectsize to used_atom